Sponge-Like Porous Manganese(II,III) Oxide as a Highly Efficient Cathode Material for Rechargeable Magnesium Ion Batteries

Here, we are the first to report a spinel type Mn₃O₄ as cathode material for Mg-ion battery (MIB) with graphite foil (Gif) as current collector. High Coulombic efficiency and good cyclic stability of Mn₃O₄ are demonstrated, and the process is enhanced by using Mn₃O₄ nanoparticles with a sponge-like morphology. The powder exhibits a network of interconnected mesopores with well-dispersed nanoparticles (∼10 nm) and large specific surface area (102 m² g^–1). This structural configuration provides easy access for electrolyte penetration which markedly enhances the utilization of electroactive material, generates high ion flux across the electrode–electrolyte interface and provides more active sites for electrochemical reactions to occur. This study can possibly open the way for exploring other similar compounds with a spinel type structure for MIB

Solvent-Controlled Charge Storage Mechanisms of Spinel Oxide Electrodes in Mg Organohaloaluminate Electrolytes

Considering the improved safety, reduced cost, and high volumetric energy density associated with Mg batteries, this technology has distinct advantages for large-scale energy storage compared to other existing battery technologies. However, the divalency of the Mg²⁺ cation cause sluggish magnesiation kinetics in crystalline host materials, resulting in poor performance with regards to capacity and cycling stability for intercalation based electrodes. Here, we present a Mg battery using Mn₃O₄ as the electrode material and Mg metal as the counter electrode in a Mg organohaloaluminate electrolyte. The reversible capacity when Mn₃O₄ was used as cathode reached ∼580 mAh g^–1 at a current density of 15.4 mA g^–1, whereas a reversible capacity of ∼1800 mAh g^–1 was obtained in an anode configuration. The Mn₃O₄ in a cathode configuration shows excellent cycling stability with no loss of capacity after 500 cycles at a current density of 770 mA g^–1. As an anode, Mn₃O₄ retained 86% of its initial capacity after 200 cycles. These exceptional charge storage properties and high cycling stability are attributed to highly reversible interfacial reactions involving the electrolyte solvents. Our conclusions are supported by density functional theory calculations in addition to quantitative kinetics analysis and scanning transmission electron microscopy combined with energy dispersive spectroscopy and electron energy loss spectroscopy

Cation Disorder in Ferroelectric Ba₄M₂Nb₁₀O₃₀ (M = Na, K, and Rb) Tetragonal Tungsten Bronzes

The crystal structure of tetragonal tungsten bronzes, with the general formula A12A24C4B12B28O30, is flexible both from a chemical and structural viewpoint, resulting in a multitude of compositions. The A1 and A2 lattice sites, with different coordination environments, are usually regarded to be occupied by two different cations such as in Ba4Na2Nb10O30 with Na+ and Ba2+ occupying the A1 and A2 sites, respectively. Here, we report on a systematic study of the lattice site occupancy on the A1 and A2 sites in the series Ba4M2Nb10O30 (M = Na, K, and Rb). The three compounds were synthesized by a two-step solid-state method. The site occupancy on the A1 and A2 sites were investigated by a combination of Rietveld refinement of X-ray diffraction patterns and scanning transmission electron microscopy with simultaneous energy-dispersive spectroscopy. The two methods demonstrated consistent site occupancy of the cations on the A1 and A2 sites, rationalized by the variation in the size of the alkali cations. The cation order–disorder phenomenology in the tungsten bronzes reported is discussed using a thermodynamic model of O’Neill and Navrotsky, originally developed for cation interchange in spinels

Origins and Importance of Intragranular Cracking in Layered Lithium Transition Metal Oxide Cathodes

Li-ion batteries have a pivotal role in the transition toward electric transportation. Ni-rich layered transition metal oxide (LTMO) cathode materials promise high specific capacity and lower cost but exhibit faster degradation compared with lower Ni alternatives. Here, we employ high-resolution electron microscopy and spectroscopy techniques to investigate the nanoscale origins and impact on performance of intragranular cracking (within primary crystals) in Ni-rich LTMOs. We find that intragranular cracking is widespread in charged specimens early in cycle life but uncommon in discharged samples even after cycling. The distribution of intragranular cracking is highly inhomogeneous. We conclude that intragranular cracking is caused by local stresses that can have several independent sources: neighboring particle anisotropic expansion/contraction, Li- and TM-inhomogeneities at the primary and secondary particle levels, and interfacing of electrochemically active and inactive phases. Our results suggest that intragranular cracks can manifest at different points of life of the cathode and can potentially lead to capacity fade and impedance rise of LTMO cathodes through plane gliding and particle detachment that lead to exposure of additional surfaces to the electrolyte and loss of electrical contact

Understanding Capacity Fading of MgH₂ Conversion-Type Anodes via Structural Morphology Changes and Electrochemical Impedance

Previous studies have demonstrated that MgH₂ is a promising conversion-type anode toward Li with high capacity (2037 mAh/g) and low discharge/charge overpotential hysteresis. A major challenge is the capacity loss after a few cycles. To improve the understanding of the complex conversion mechanism at the electrode/electrolyte interface and of its possible evolution, a systematic investigation of the morphology–property relation is undertaken. A multitude of MgH₂ materials are obtained by mechanical milling using different devices, milling conditions, and time intervals. Upon cycling, the performance of the assembled batteries is strongly dependent on the quality of the prepared MgH₂ powders. Electrochemical discharge/charge profiles (MgH₂ ⇆ 2LiH + Mg) are discussed according to the changes in microstructure and morphology revealed by powder X-ray diffraction and transmission electron microscopy. For all electrode composites, the loss of the capacity occurs typically during delithiation in agreement with a kinetically limited process, namely, of LiH “detachment”. Electrochemical impedance spectroscopy is meaningfully carried out using the representative tape-casted electrodes in Li/MgH₂ cells to monitor the evolution of resistance components, in particular the formation of a solid electrolyte interphase (SEI)-like layer as a function of particle size, state of charge, and cycle number